This invention relates to a flat-type fluorescent display device incorporating field emission cathodes (hereinafter referred to as "FECs") therein as an electron source, and more particularly to a flat-type fluorescent display device which is relatively increased in size of an image plane and relatively decreased in picture cell density for display by means of the FECs.
Now, a conventional flat-type fluorescent display device incorporating FECs therein will be described with reference to FIG. 7. The conventional fluorescent display device includes a substrate 100, on which cathodes 101 are deposited. On the cathodes 101 are formed insulating layers 102 and gate electrodes 103 in turn. The insulating layers 102 and gate electrodes 103 are formed with holes 104 by photolithography and etching. The cathodes 101 each are formed on a portion thereof exposed through each of the holes 104 with an emitter 105 of a conical shape, resulting in FECs 110 being formed. The fluorescent display device also includes a transparent or light-permeable front cover 106 arranged opposite to the substrate 100. The front cover 106 is formed by deposition on an inner surface thereof with a transparent light-permeable anode conductor 107, which is formed by deposition on portions thereof opposite to the FECs with phosphor layers 108, resulting in anodes 109 which function as a luminous display section being formed.
In the conventional fluorescent display device constructed as described above, electrons discharged from the FECs 110 impinge on the anodes 109 to permit the phosphor layers 108 of the anodes to emit light, which is then observed through the anode conductor 107 and front cover 106.
Thus, it will be noted that the flat type conventional fluorescent display device using the FECs is a front emission type which is adapted to permit luminescence of the phosphor layers to be observed through the anode conductor and front cover. The reason why the front emission type fluorescent display device has been employed is that it is highly difficult to form the insulating layers 102 and emitters 105 of the FECs of a transparent or light-permeable material, so as to provide a construction which permits the luminescence to be observed through the substrate 100.
The fluorescent display device incorporating the FECs therein is generally used for graphic display. Such applications cause the number of electrode lines to be increased, wherein the electrode lines are driven while being scanned in order. Unfortunately, this causes a duty ratio of the device to be reduced, leading to a decrease in luminance.